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If the buffer is small enough to fit in the cache then >> it cannot be expected that the benchmark will generate much memory >> bandwidth. For example, on a system with 320MB L3 cache the existing >> hardcoded default of 250MB is insufficient. >> >> Use the measured cache size to determine a buffer size that can be >> expected to trigger memory access while keeping the existing default >> as minimum that has been appropriate for testing so far. >> >> Signed-off-by: Reinette Chatre >> --- >> Changes since V1: >> - Ensure buffer is at least double L3 cache size. (Ilpo) >> - Support user override of default buffer size. (Ilpo) >> --- >> tools/testing/selftests/resctrl/mba_test.c | 8 +++++++- >> tools/testing/selftests/resctrl/mbm_test.c | 8 +++++++- >> 2 files changed, 14 insertions(+), 2 deletions(-) >> >> diff --git a/tools/testing/selftests/resctrl/mba_test.c b/tools/testing/selftests/resctrl/mba_test.c >> index 7e43056c8737..d8d9637c1951 100644 >> --- a/tools/testing/selftests/resctrl/mba_test.c >> +++ b/tools/testing/selftests/resctrl/mba_test.c >> @@ -182,7 +182,13 @@ static int mba_run_test(const struct resctrl_test *test, const struct user_param >> fill_buf.memflush = uparams->fill_buf->memflush; >> param.fill_buf = &fill_buf; >> } else if (!uparams->benchmark_cmd[0]) { >> - fill_buf.buf_size = DEFAULT_SPAN; >> + unsigned long cache_total_size = 0; >> + >> + ret = get_cache_size(uparams->cpu, "L3", &cache_total_size); >> + if (ret) >> + return ret; >> + fill_buf.buf_size = cache_total_size * 2 > DEFAULT_SPAN ? >> + cache_total_size * 2 : DEFAULT_SPAN; >> fill_buf.memflush = 1; >> param.fill_buf = &fill_buf; >> } >> diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c >> index b1f03a73333f..7635ee6b9339 100644 >> --- a/tools/testing/selftests/resctrl/mbm_test.c >> +++ b/tools/testing/selftests/resctrl/mbm_test.c >> @@ -149,7 +149,13 @@ static int mbm_run_test(const struct resctrl_test *test, const struct user_param >> fill_buf.memflush = uparams->fill_buf->memflush; >> param.fill_buf = &fill_buf; >> } else if (!uparams->benchmark_cmd[0]) { >> - fill_buf.buf_size = DEFAULT_SPAN; >> + unsigned long cache_total_size = 0; >> + >> + ret = get_cache_size(uparams->cpu, "L3", &cache_total_size); >> + if (ret) >> + return ret; >> + fill_buf.buf_size = cache_total_size * 2 > DEFAULT_SPAN ? >> + cache_total_size * 2 : DEFAULT_SPAN; >> fill_buf.memflush = 1; >> param.fill_buf = &fill_buf; >> } >> > > It has a bit of code duplication feel in it so I'd consider adding > something like ssize_t get_default_span() (perhaps there exists a better > name for it that is not "span" based). Also DEFAULT_SPAN is no longer > truly the default span. Good suggestion. How about get_fill_buf_size()? Regarding the "DEFAULT_SPAN" it seems to have some 'magic number smell' to it. When I tried to eliminate it and only rely on cache size the tests were failing on some earlier platforms with smaller L3. I then started treating it as a minimum in order to keep original behavior on these earlier systems. Perhaps renaming it to "MINIMUM_SPAN" would make this change clear? > > But neither is the end of the world as is... > > Reviewed-by: Ilpo Järvinen > > Thank you very much. Reinette